From a theoretical viewpoint, the reaction which occurs at the positive plate in a lead-acid battery shows that every gram of lead dioxide should yield 0.224 ampere hour of useful electrical capacity. However, as is also well known, in actual practice only 30-50% of this capacity is realized in conventional lead-acid batteries. This relatively low efficiency remains the conventional practice despite considerable efforts to provide commercially viable ways of achieving higher efficiencies.
Likewise, the concept of doping lead oxides with particular materials to improve certain operating characteristics of lead-acid batteries has been suggested. For example, U.S. Pat. No. 3,723,182 to Venuto discloses the addition of minor amounts of a uniformly dispersed quantity of an antimony throughout the lead peroxide active material. The antimony is believed bound in a molecular array with the lead and oxygen. Batteries built with positive electrodes using such active material were shown to be free of the defects usually associated with batteries using non-antimony lead grids, including the ability to accept charge at any stage of discharge, improved capacity and cycle life equal to that of batteries having antimonial lead grids.
It is likewise known that certain impurities may also have deleterious effects on the characteristics of lead-acid batteries. For this reason, the purity of the lead oxide and sulfuric acid used in the preparation of lead sulfate paste is of particular importance since such impurities are likely to contaminate the electrolyte or active part of the battery electrode. Accordingly, impurities such as silver, copper, aluminum, iron, zinc, manganese and others which are believed to have a deleterious effect on the electrical performance of electrochemical cells are commonly carefully controlled. As an example, U.S. Pat. No. 3,788,898 to Yarnell states that such impurities should not be present in quantities greater than 0.3 mol percent.
Some investigators have also examined the possibility of increasing the copper content in alloys used for forming grids for use in lead-acid batteries. Thus, Korov and Denev, in Metalurgiya (Bulgaria) 1972, 27, (5) 22-25, "Investigation of the Possibilities for Increasing the Copper Content of (Lead) Battery Alloys, concluded that adding copper within a certain range to pre-eutectic lead-antimony alloys has a positive effect both on the physical and mechanical properties of the alloys, as well as on their hardness and castability. The authors further note that the significant improvement in the mechanical properties of the battery grid made using such alloys means increased stability of the battery in heavy-duty applications while the reduced rate of corrosion increases the life of the battery.
Further, various studies have likewise speculated that the active material in a lead-acid battery becomes doped by the transport of an element or elements from the grid into the oxide active material in the normal service of the battery and that this can affect the performance characteristics of the battery. In particular, Burbank, J. Electrochem. Soc., Vol. 111, No. 10. page 1112, Oct. 1964, concludes that the presence of antimony in the positive grid exerts the direct and beneficial influence of causing prismatic PbO.sub.2 formation in the active material and consequently aids in the retention of a firm paste texture and cell capacity in shallow cycle test.
U.S. Pat. No. 4,329,408 to Mao et al. is predicated on the discovery that the performance of lead-acid batteries can be improved by utilizing a lead oxide incorporating a minor amount of copper. At a minimum, the '408 patent teaches utilizing at least 0.01% by weight, based upon the total weight of the lead oxide, while it is preferred to utilize no more than about 0.06 or perhaps 0.07% by weight copper. While it is preferred to utilize copper as a doping agent due to the demonstrated advantages derived, Mao et al. also state that it is believed that other elements, such as lithium, bismuth, barium, phosphorous, silver, aluminum and calcium, should have similar doping effects and may be substituted for the copper, if desired. If used, the amount of such elements should not be in significant excess of the dopant-lead rich eutectic. (Column 4, lines 5-10).
The prior art also includes a number of patents disclosing alloys used for grids and the like in which the alloying ingredients include one or more of copper, antimony and tin. These include U.S. Pat. No. 2,252,104 to Walde, U.S. Pat. No. 3,309,228 to Dodson et al., U.S. Pat. No. 3,990.893 to Nijhawan et al., U.S. Pat. No. 3,993,480 to Ueberschaer et al., U.S. Pat. No. 4,158,563 to Hebbar et al., U.S. Pat. No. 4,230.779 to Varma, U.S. 4,279,977 to Matter, U.S. 4,376,093 to Prengaman, U.S. 4,456,579 to Rao et al., and U.S. 4,708,918 to Fitzgerald et al.
Despite the considerable efforts of the prior art, there remains the need to be able to provide lead oxide materials of even higher efficiency. Thus, lead-acid battery manufacturers are being called upon to provide batteries with ever-increasing efficiency. In this regard, it would be considered significant to be able to provide an efficiency increase of 6% and higher.
It is accordingly a principal object of the present invention to provide a novel lead oxide capable of imparting improved performance characteristics to lead-acid batteries having active material made from such an oxide.
A related and more specific object provides a lead oxide capable of achieving increased efficiency of oxide utilization in a lead-acid battery using such an oxide.
Yet another object lies in the provision of the novel oxide capable of increasing, in a lead-acid battery using such an oxide, the electrical conductivity of the system so as to provide lower internal resistance and thus higher power output.
A still further object of this invention is to provide a lead oxide capable of imparting improved cycle life to lead-acid batteries using such an oxide.
Another object provides a lead oxide which can be readily made by techniques commonly employed for making conventional lead oxides.
Other objects and advantages of the present invention will become apparent as the following description proceeds.